Conventionally, a PLC (Programmable Logic Controller) for controlling an industrial machine or the like installed in a production line of a factory has been known.
The PLC is provided with a CPU unit for controlling the PLC, an input unit to which a signal from a sensor is inputted, and an output unit for outputting a control signal to an industrial machine or the like. The CPU unit has a memory for storing a user program for controlling the industrial machine or the like. This user program is configured so as to be editable by a tool device connected to the CPU unit.
Moreover, in the PLC, a process for acquiring a signal inputted to the input unit in the memory of the CPU unit, a process for executing the user program, a process for writing execution results (operation results) of the user program in the memory and for sending them to the output unit, and a peripheral process for transmitting and receiving data to and from the tool device are executed repeatedly. Thus, the PLC can control an industrial machine or the like based upon an input from the sensor.
Moreover, conventionally, a PAC (Programmable Automation Controller) provided with high degree software functions of a personal computer and reliability of PLC has been known (for example, see Patent Document 1).
The PAC of the above-mentioned Patent Document 1 is configured such that a plurality of tasks are executed in parallel with one another in a time sharing manner, with each task of the plurality of tasks being executed based in cycles based on each task. That is, in the PAC, multitask processes are carried out. In this case, each task includes an execution of a user program in accordance with the corresponding task, and the like.    Patent Document 1: Japanese Unexamined Patent Publication No. 2009-181443